This invention relates to electromagnetic projectile launching systems and more particularly to such systems which include means for controlling the initial rate of current injection into a pair of projectile launching rails.
Electromagnetic launchers accelerate projectiles by passing a large current through a pair of projectile launching rails and an associated sliding conductive armature mounted between the rails. This current flow results in an accelerating force on the armature which can be used to propel an associated projectile along the conductive rails. Because of the massive currents involved and the initially low armature velocity, excessive heat may be locally generated in the rails, particulary near the breech region, during the initial moments of armature acceleration. This excessive heat generation can result in melting of the rail surface material which will quickly deteriorate the rail contact areas.
Computer calculations have shown that substantially lower breech rail surface temperatures will result if a projectile armature is already moving at a low velocity before flow of the propelling current commences. The primary reason for these lower surface temperatures is that at peak current, the rails and armature are subjected, at their interface, to a peak thermal flux for a given time period which is dependent upon the residence time of the armature. For faster armature movement, the rail surfaces experience this thermal flux for a shorter time and, therefore, the rails are subject to a lower surface temperature rise.
Lowering the maximum rail surface temperature will increase the life of the rails and barrel, and it is particularly important to prevent the possibility of temperature excursions to the melting point of the rail surface material. Launchers have been proposed in which a resistor is connected in series with the projectile launching rails to prevent excessive premature heating of the armature and to prevent premature armature movement during the period when current builds up in an inductive type current source. Examples of these launchers can be found in U.S. Pat. No. 4,355,561, issued Oct. 26, 1982 to Kemeny et al. and U.S. Pat. No. 4,369,691, issued Jan. 25, 1983 to Baehr, Jr. et al. The disclosures of these Patents are hereby incorporated by reference.